body {
  font-family: "Source Han Sans", "San Francisco", "PingFang SC", "Hiragino Sans GB", "Droid Sans Fallback", "Microsoft YaHei", sans-serif;
  transition: background-color .2s;
}

#header {
  position: fixed;
  top: 0;
  left: 0;
  height: 50px;
  right: 0;
  
  background-color: #333;
  color: #fff;
  font-size: 20px;
  
  line-height: 50px;
  display: inline-block;
  vertical-align: middle;
  padding-left: 15px;

  overflow: hidden;
  z-index: 0;
}

.container {
  position: fixed;
  top: 50px;
  left: 0;
  height: calc(100vh - 50px);
  right: 0;

  margin: 0 auto;
  display: block;

  transition: 0.2s;
  overflow: hidden;
  z-index: 0;
}
